Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Balance
Beginning Balance, shares at Dec. 31, 2015		344,855,704
Balance, beginning of period at Dec. 31, 2015	$ 1,839,654	$ 3,449	$ 1,328,561	$ 8,961,985	$ (615,205)	$ (7,839,136)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	692,164			692,164
Total other comprehensive income (loss), net of tax	49,824				49,824
Dividends	(252,321)			(252,321)
Repurchase of common stock	(465,341)					(465,341)
Share-based compensation and 401(k) match made with Treasury shares	39,826		36,956			2,870
Issuance of nonvested stock (in shares)		272,479
Issuance of nonvested stock	0	$ 2	(2)
Exercise of stock options (in shares)		466,871
Exercise of stock options	15,782	$ 5	15,777
Tax benefit of equity awards	570		570
Retirement of treasury stock (in shares)		(165,000,000)
Retirement of treasury stock	0	$ (1,650)		(8,064,155)		(8,065,805)
Ending Balance, shares at Dec. 31, 2016		180,595,054
Balance, end of period at Dec. 31, 2016	1,920,158	$ 1,806	1,381,862	1,337,673	(565,381)	(235,802)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	521,759			521,759
Total other comprehensive income (loss), net of tax	65,332				65,332
Dividends	(251,862)			(251,862)
Repurchase of common stock	(465,263)					(465,263)
Share-based compensation and 401(k) match made with Treasury shares	42,800		29,600			13,200
Issuance of nonvested stock (in shares)		408,950
Issuance of nonvested stock	0	$ 4	(4)
Exercise of stock options (in shares)		282,543
Exercise of stock options	$ 11,353	$ 3	11,350
Retirement of treasury stock (in shares)	(165,000,000)
Ending Balance, shares at Dec. 31, 2017		181,286,547
Balance, end of period at Dec. 31, 2017	$ 1,844,277	$ 1,813	1,422,808	1,607,570	(500,049)	(687,865)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	531,451			531,451
Total other comprehensive income (loss), net of tax	(21,287)				(21,287)
Dividends	(245,810)			(245,810)
Repurchase of common stock	(390,606)					(390,606)
Share-based compensation and 401(k) match made with Treasury shares	46,375		33,293			13,082
Issuance of nonvested stock (in shares)		485,005
Issuance of nonvested stock	$ 0	$ 4	(4)
Exercise of stock options (in shares)	160,000	159,673
Exercise of stock options	$ 3,525	$ 2	3,523
Reclassification of certain tax effects (Note 1)	0			108,348	(108,348)
Cumulative effect of change in accounting (Note 1) (Accounting Standards Update 2014-09) at Dec. 31, 2017	6,024			6,024
Ending Balance, shares at Dec. 31, 2018		181,931,225
Balance, end of period at Dec. 31, 2018	$ 1,773,949	$ 1,819	$ 1,459,620	$ 2,007,583	$ (629,684)	$ (1,065,389)